JP2011501637A - Rotor for electric motor, electric motor, dental handpiece - Google Patents

Abstract

A rotor for an electric motor, the rotor having a shaft (20) having a rotation axis (80) and at least one magnet (40) disposed around the rotation axis (80). A rotor comprising a centering element (60, 60 ′, 60 ″, 60 ′ ″) elastically connected to the shaft (20) or configured as part of the shaft 20 The centering element (60, 60 ′, 60 ″, 60 ′ ″) externally attaches a magnet (40) to center it with respect to the rotational axis (80) of the shaft (20). It is characterized by pressing.
[Selection] Figure 3

Description

  The present invention relates to a rotor for an electric motor, a corresponding electric motor, and a dental handpiece comprising such an electric motor.

As illustrated in FIG. 5, the rotor of an electric motor, for example constituted by a collectorless electric motor, usually consists of a shaft 20 on which two balancing rings 100, Magnets are arranged between 100 '.
The two ball bearings 70 arranged on the shaft 20 around the two balancing rings 100, 100 ′ are effective as bearings.
The rotational movement of the rotor occurs around the axis of rotation 80 of the shaft 20 and can be further transmitted from the shaft 20 to either a coupling system or a gear to a further shaft.
The balancing rings 100, 100 ′ have the effect of compensating for rotor imbalance at two levels.

Such collectorless electric motors are used, for example, for driving dental instruments, for example for dental handpieces, for example in motorized dental angled parts.
A dental handpiece 1 of this kind with a corresponding electric motor 10 is illustrated in FIG.

The higher the maximum speed of the rotor, the more important is the quality of balancing the rotor and the degree of concentricity or radial swing of the components.
Unbalance leads to increased distortion of the ball bearing 70 and generation of strong noise.

  According to the prior art, in this situation, the fit between the balancing rings 100, 100 ′ and the shaft 20 is such that the rotation axes of the aforementioned components are aligned as much as possible or with as little deviation as possible. For this reason, it is known to be configured as a press fit or a press bond.

Corresponding press fits between the rotor magnet 40 and the shaft 20 are not well done, but are made especially for two reasons as described below: First, used to make a suitable magnet The resulting material is friable to a certain degree and tends to tear above a certain tensile load.
To some extent, tensile loads will already occur when the magnet is pressed.
Furthermore, when rotating, centrifugal force is generated, which also results in a tensile load on the magnet.
Considering the whole, the load of the magnet is sensuously very large.
Secondly, the coefficient of thermal expansion of the material forming the shaft, for example iron, is considerably different from that of the material normally forming a magnet.
Generally, a magnet has less thermal expansion than a shaft.
For this reason, when a magnet is press-fitted to the shaft, there is a risk that the magnet will be torn or ruptured to some extent when heated.

According to the interrelation described in the prior art, it is customary for the magnet 40 to be bonded to the shaft 20, so that the adhesive 24 is formed for that purpose.
The adhesive 24 causes a bonding gap at a place where the bonding is performed.
This adhesive 24 avoids very large tensile stresses, and the adhesive layer of adhesive 24 located in the adhesive gap compensates for the different expansion effects, one of which is shaft 20 and the other is magnet 40.

However, this technique still not only accurately centers the magnet 40 on the shaft 20, particularly the cross-misalignment where the symmetry axis of the magnet 40 intersects the rotational axis 80 of the shaft 20, There is a problem of bonding to the center so as to be diagonal.
In order to keep the possible errors caused by this as small as possible, in this case it is therefore further possible to make the size of the bonding gap provided between the magnet 40 and the shaft 20 as small as possible. Well done.
Conversely, this results in narrow manufacturing tolerances for the magnet 40 and shaft 20, and further allows the use of adhesive means, particularly at low viscosities.
Therefore, it should be expected that the adhesive gap of the adhesive 24 is formed more or less asymmetrically with respect to the rotation axis of the shaft 20.
The resulting concentric error or the resulting unbalanced result then needs to be balanced later.
The surface of the magnet 40 may be ground again after bonding and before balancing the shaft.
The effect of this is due to the fact that the shaft 20 extends virtually straight on the outside of the magnet 40, but the asymmetry of the adhesive gap cannot be removed in this way.
The quality of the coaxiality between the magnet 40 and the shaft 20 is easily understood, but depends on the thickness of the adhesive gap.
The larger the gap, the greater the misalignment and the greater the “inner” imbalance.

  As the speed increases, the quality of the balance plays an increasing role in the quality of the rotor, so at very high speeds an “inner” imbalance, ie one in close proximity to this kind of axis, “inner “Unbalance is also very disturbing.

Further known from the prior art is to reinforce part of the balancing ring or the rotor magnet surrounding the magnet, like a sleeve.
This type of reinforcement contributes to protecting the magnet, for example from corrosion or rupture, but does not have any effect on the problems mentioned above.
This aforementioned reinforcement is adhered to the magnet.

It is an object of the present invention to provide a rotor that can be made particularly accurate and at the same time facilitate the centering of magnets.
The corresponding purpose is to set up an electric motor with such a rotor and a corresponding dental handpiece with such an electric motor.

This object is achieved by the respective object of the independent claims.
Preferred embodiments are provided by the dependent claims.

In accordance with the present invention, a rotor for an electric motor is provided, the rotor having a shaft with a rotating shaft and at least one magnet disposed about the rotating shaft.
In addition, the rotor has a centering element that is elastically connected to the shaft and configured as part of the shaft, the centering element being external to center it with respect to the axis of rotation of the shaft. Press the magnet.

Since the centering element presses the magnet from the outside to center it, the magnet is not against the rotating shaft due to the adhesive gap between the shaft and the magnet as compared with the prior art. Accurate alignment is not possible.
Therefore, achieving accurate alignment becomes easier.
Furthermore, the pressure of the centering element acting on the magnet from the outside acts on the magnet in the opposite direction to the centrifugal force during rotation.
By this method, high speed is achieved without the magnet surface exceeding a critical tensile stress.
Furthermore, by providing the rotor according to the present invention, it is possible to design a larger adhesion gap between the shaft and the magnet than in the prior art, and in comparison with the prior art, the adhesive having higher viscosity. Material can be used.
This is an advantage that this type of adhesive may have a higher adhesive strength and is easier to manufacture.
Furthermore, the centering element provides a means of protection in case the adhesive force between the shaft and the magnet is lost.
The compressive force of the centering element acting on the magnet can be easily selected in an efficient way to transmit the torque acting on the magnet through the centering element to the rotor shaft.

  Preferably, in the rotor, the magnet is disposed on the outer periphery outside the shaft.

  Preferably, the centering element and the magnet are at least partially connected to each other by a press fit or a shrink fit.

  Preferably, the centering element has a sleeve-like region that at least partially wraps around the magnet from the outside. This sleeve-like region may have a cylindrical inner wall, the diameter of which, in a way, corresponds to a limited surface of the magnet, for example the outer side of the magnet, by a pressing or contracting connection.

  Preferably, the rotor further comprises at least one balancing ring disposed on the shaft, and the centering element is elastically connected to the balancing ring.

The centering element and the balancing ring may in this case be formed from one piece.
A centering element may in this case be provided that presses the balancing ring or contracts the balancing ring.

  Preferably, the balancing ring is in this case either pressed against the shaft or contracted on the shaft.

Preferably, the centering element envelops the magnet along the shaft and covering the entire area of the magnet.
However, the centering element may be provided so as to enclose the magnet so as to cover only a part of the entire range of the magnet along the shaft.

  Preferably, an adhesive is provided between the shaft and the magnet.

  According to a further aspect of the present invention, an electric motor is provided having a rotor according to the present invention.

  According to a further aspect of the present invention, a dental handpiece is provided having the electric motor of the present invention.

  The invention is explained in more detail below using embodiments and with reference to the drawings.

FIG. 1 shows an illustration of a dental handpiece envisioned for use with an electric motor in the present invention. FIG. 2 shows a partial illustration of the rotor of the first aspect of the present invention. FIG. 3 shows a partial illustration of the rotor of the second aspect of the present invention. FIG. 4 shows a partial illustration of the rotor of the third aspect of the present invention. FIG. 5 shows a partial illustration of a rotor in the prior art.

A handpiece, schematically illustrated in FIG. 1 and generally given as reference number 1, in which an electric motor according to the invention is used, has an extended handle casing 2, which is rearward. The region 2a and the front region 2b are divided, and the two regions 2a and 2b are surrounded by an angle α of about 155 ° to 170 °.
The operation of the handpiece 1 in the patient's mouth is simplified by this angled design.
However, in this regard, the method of using the electric motor in the present invention described in more detail below is not limited to so-called angled handpieces.
Rather, this motor can be commonly used in handpieces for dentistry, dental medicine or dental technology.

The front end of the handle casing is the head region of the handpiece 1 having a tool holder 5 that is rotatably held by two bearings 6a, 6b.
This tool holder is in particular provided to receive a dental drill.
For ergonomic reasons, the head area 3 is designed so that the longitudinal axis I of the tool holder 5 surrounds the axis II of the region 2b at the front end of the handle casing with an angle β of about 100 °. Can be further provided.
In this case, the tool holder 5 is designed to rotate with the help of the motor 10 and will be described in more detail below, but the rotation of the motor 10 is via a drive shaft 15 extending in the front handle caging region 2b. Communicated.
In this case, the drive shaft 15 is rotatably held by two bearings 16a and 16b and is connected to the rotor 11 of the motor 10 via a transmission element 17 at the rear end thereof, and at the front end thereof. Furthermore, it is connected to the tool holder 5 via a transmission element 8.

At the rear end of the handle casing 2, the handle casing is connected to the connection portion 30 of the supply pipe 31.
This tube 31 follows the supply device (not shown) of the dental treatment center and provides the necessary medium for treatment in order to make the handpiece 1 available.
This medium is in particular the electricity used to operate the motor.
Additional processing media such as air and / or water can also be guided to the handpiece 1 via the tube 31.
The connection of the handpiece 1 is then made via a connection to the pipe connection 30 via the coupling element 4 located at the rear end.

FIG. 2 shows a portion penetrating the rotor in the first embodiment of the present invention.
The rotor includes a shaft 20 having a rotation shaft 80 and at least one magnet 40 disposed around the rotation shaft 80.
In this case, the magnet 40 has at least one pole pair that exerts an effect on the outside.

The magnet 40 has a cylindrical outer surface, hereinafter referred to as a side surface, which is symmetrical with respect to the outer surface and has a cylindrical inner direction having a diameter of this cavity corresponding to the outer diameter of the shaft 20. As a result, the magnet 40 can be disposed on the shaft 20.
Therefore, in this embodiment, the magnet 40 is disposed on the outer peripheral portion of the shaft 20.

  The more accurate the concentricity of the side facing the internal cavity of the magnet 40, the more effective the present invention will become, as will become apparent from the interrelationship described below.

The rotor is arranged in the electric motor via two bearings, which are known per se as ball bearings 70, for example.
The electric motor may be provided as a dental handpiece, for example, to drive the electric motor 10 and the dental tool itself depicted in FIG.

As depicted in FIG. 2, the rotor has a centring element 60 that is resiliently connected to the shaft or configured as part of the shaft 20.
The centering element 60 presses the magnet 40 from the outside in order to center it with respect to the rotational axis of the shaft 20.

Centering element 60 and magnet 40 are connected to each other in this embodiment by a press or press bond 22 '.
A connection by means of a shrink (shrink) fit may be provided.
In this case, the pressure coupling 22 ′ is provided on the surface of the magnet 40 facing outward—relative to the axis of rotation 80.
In this way, the centering element 60 can act on or press the magnet 40 from the outside.

The centering element 60 has a cylindrical self-playing space on the inner side, and in the meaning of press fitting, matches the outer diameter of the magnet 40, in other words, the inner diameter of the magnet 40. And consists of a sleeve-like region.
Thus, the centering element 60 or sleeve-like region is shaped like a ring and encloses the magnet 40 from the outside.
The centering element 60 is here arranged with respect to the shaft 20 rotational axis 80 in a cylindrically aligned free space symmetrical manner with respect to the rotational axis 80.

In addition, the rotor consists of a balancing ring 100 arranged on the shaft 20 directly adjacent to the magnet.
In the first embodiment shown in FIG. 2, the centering element 60 is elastically connected to the balancing ring 100 and is substantially formed of the balun syring 100 and one piece.
Therefore, the centering element 60 is configured as an extension such as the barrel of the balancing ring 100.
Alternatively, the centering element 60 can be pressed or shrunk (reduced) by a balancing ring 100 formed by a suitably sized sleeve with a cylindrical inner diameter.

  In this case, the sleeve-like region of the centering element 60 is directed so that the inner cylindrical free space is symmetrical with respect to the axis of rotation 80 when the balancing ring 100 is overlaid, so Is arranged.

This time, the balancing ring 100 is pressed or shrunk against the shaft 20.
In the first aspect, the resilient connection between the centering element 60 and the shaft 20 is made by this method.
The elastic connection between the centering element 60 and the shaft 20 is made by this method.
Since the connection between the centering element 60 and the shaft 20 is in this case elastic, the centering element 60 is relative to the axis of rotation 80 or to the shaft 20 when rotation of the rotor is provided. It is possible to form a support for the magnet 40 that fixes the position of the magnet 40 as accurately as necessary.

Briefly summarized, the joint between the outer limiting surface of the magnet 40 and the inner limiting of the sleeve-like region of the centering element 60 is configured as a press fit.
In this way, the magnet 40 can be arranged concentrically with respect to the balancing ring 100.
Similarly, since the balancing ring 100 is fixed to the shaft 20 by press fitting, the centering of the magnet with respect to the rotation axis 80 of the shaft 20 becomes particularly easy and accurate at the same time.
Instead of or in addition to the press-fit, a corresponding shrinkage connection, in other words a shrinkage fit, is also possible.

Thereby, in general terms, the centering element is elastically fixed to the shaft, and this connection need not have to be made via a balancing ring.
For example, the centering element may also be provided in its base region, which itself is configured like a barrel with a central cavity, which cavity is provided directly as a shaft connection.
Thereby, in this case, the centering element is press-fit or shrink-fit directly against the shaft.
In this case, for example, the centering element may be arranged on the shaft directly adjacent to the magnet.
A balancing ring may then be provided on the other side of the centering element.

As the first aspect shows, two balancing rings 100, 100 ′ disposed on the shaft 20 on both sides of the magnet 40 are provided.
The second balancing ring 100 ′ is configured symmetrically with the first balancing ring 100, so that a second lancing ring 100 is therefore provided, and at the same time the two balancing rings 100, 100 ′ are Again, it is elastically fixed to the centering elements 60, 60 ′.
By having two such centering elements 60, 60 ′, the accuracy of the centering of the magnet 40 with respect to the rotation axis 80 can be further increased.

In the first embodiment, the centering elements 60, 60 ′ are configured in such a way that they wrap completely around the magnet 40 in the assembled state; in other words, those in the sleeve-like region covering the magnet 40. At the end face 45 of the two, they are in strong contact with each other or directly adjacent to each other.
Therefore, in this case, the magnet 40 is completely enclosed, so that additionally a centering function, eg a safety function against the magnet 40 being broken or ruptured, is achieved by the centering elements 60, 60 ′. .

  The adhesive 24 ′ is provided between the shaft 20 and the magnet 40 in the first aspect.

  The inner diameter of the magnet 40 is formed symmetrically with the limit surface in the outer direction of the magnet 40, in other words, the side surface, and the limit surface in the outer direction of the shaft 20 is also configured symmetrically with the rotation axis 80. The gap between the magnet 40 and the shaft 20 that is necessary for the bonding of the adhesive 24 needs to be equal in strength and symmetrical with respect to the rotation axis 80 at all points by the apparatus of the present invention. .

  Thus, in particular, the occurrence of axial misalignment between the magnet 40 and the shaft 20 can be eliminated, and therefore no corresponding imbalance occurs.

The device according to the invention has an additional advantage with respect to the absolute width of the adhesive gap of the adhesive 24 ′ between the magnet 40 and the shaft 20.
Compared to the prior art described above, the centering of the magnet 40 must no longer be done with as little gap as possible, and a wider gap can be selected, a further result of this compared to the prior art. It makes it possible to use more viscous adhesives, in other words, adhesives that also have higher adhesive strength and / or better manufacturability.

The compressive stress generated in the magnet 40 by the two centering elements 60, 60 'also has a more advantageous effect.
The critical speed at which the magnet 40 does not function mechanically due to centrifugal force is increased by the compressive stress caused by the centering element.
Therefore, the tensile stress caused by centrifugal force can be reduced by the centering element.

The safety protection against rupture or rupture of the magnet 40 at a specific operating speed is increased by this method.
Thus, for example, the mechanical parameters of the material of the magnet 40 can be varied to be more absorbed.

Thus, this method allows a particularly high speed without the surface of the magnet 40 exceeding the critical tensile tension. Again in this respect, the centering elements 60, 60 'are provided as a first embodiment completely. It is beneficial to incorporate such a magnet 40-in other words, covering the entire range of the magnet 40 along the rotation axis 80.

In addition, the present invention provides a security feature against the reduction in adhesion strength between the shaft 20 and the magnet 40, since it is between the centering elements 60, 60 'and the magnet. This is because the strength of the compression force passing through the crimp 22 ′ is sufficient to efficiently transmit torque from the magnet 40 to the shaft 20.
Therefore, the present invention does not directly provide the mechanical connection provided between the inner cavity of the magnet 40 and the region of the outer surface of the shaft 20 located in this cavity. Even if it works.

The centering element 60 may be designed in such a way as to perform a reinforcing function, in other words providing a protection from the magnet 40 being destroyed.
This can be accomplished by appropriately selecting the appropriate material for the centering element and adaptively selecting the thickness and shape.

In FIG. 3, a second aspect is shown.
Differences from the first aspect will be described below.

In a second aspect, a centering element 60 ″ is provided that covers the upper side of the magnet 40 along the axis of rotation 80 and covers all its longitudinal extent.
A push coupling 22 or a shrink coupling is again provided between the centering element 60 ″ and the magnet 40.

In the region where the centering element 60 '' protrudes so as to cover the magnet 40 on both sides, the centering element 60 '' in each case is connected to one of the balancing rings 100, 100 ′ and again to the pressure coupling 26 ′. And is connected in an elastic manner.
Alternatively, the centering element 60 ″ may be contracted on the two balancing rings 100, 100 ′.

The two balancing rings 100, 100 'are in each case elastically coupled on the shift via a press fit 28'.
Alternatively, the balancing ring 100, 100 ′ may be contracted on the shaft 20.

Compared to the first aspect, here, therefore, one centering element 60 ″ is provided, which projects over the magnet 40.
The centering element 60 ″ forms a centering sleeve over the two balancing rings 100, 100 ′, so to speak.

  The centering element 60 ″ is elastically fixed to the shaft 20 via the balancing rings 100, 100 ′ so that the more advantageous centering effect on the magnet 40 can be achieved again.

  Furthermore, the continuous design of the centering element 60 ″ allows for an especially good safety compensation function, because it is gapd at the level of the magnet 40—with respect to the longitudinal extent of the rotary shaft 80. It is because it is formed without.

  The adhesive 24 ′ may again be provided between the magnet 40 and the shaft 40.

In order to manufacture the rotor, in this case the first magnet 40 is pressed into the centering element 60 '' or into the centering sleeve, and in the subsequent step, the components formed thereby are Two balancing rings 100, 100 that are pressed or shrunk with both the centering sleeve and the shaft 20 are then press fit into the applied shaft 20 and in a further subsequent step.
In the last-mentioned step, the centering element 60 ″ is centered with respect to the shaft 20, and therefore the magnet 40 is also centered with respect to the shaft 20.
In this case, this is advantageous if an adhesive with a suitably long duration can be selected.

In the first aspect, the connection between the centering element 60 ″ and the shaft 20 need not necessarily be made via the balancing ring 100 or the two balancing rings 100, 100 ′.
Instead of the balancing rings 100, 100 ′, components correspondingly formed in the shape of a symmetrical ring may be provided.

In FIG. 4, a third aspect is shown. Here again, as in the first embodiment, two centering elements 60 '''are provided, in which case the centering elements 60''' are elastically connected to the balancing ring, in other words, for example- As shown in FIG. 4—in either case, this centering element 60 ′ ″ is formed from a single piece with the individual balancing rings 100, 100 ′.
Alternatively, the connection can again be provided by a push connection, contraction.

Compared to the first embodiment, in the overlaid state, the two centering elements 60 ''', however, do not extend along the axis of rotation 80 to the entire longitudinal extent of the magnet 40, however The magnet 40 is encased only in the area of the individual bridge.
Due to the symmetrical relationship, the centering function of the centering element 60 '''is performed here.
The advantageous effect of compressive stress acting on the magnet 40 from the outside is that it covers a smaller area compared to the first embodiment, but does not act on the two regions at the end of the magnet 40 and is particularly sensitive. The corner positions that tend to get rid of are correct here.

  In all aspects, a different ring-like element or a plurality of different ring-like elements may be used in place of the balancing ring 100 or the plurality of balancing rings 100, 100 '.

The coaxial action of the electric motor can have an advantageous influence on the present invention, and this effect gains a demanded advantage in increasing speed, and the present invention is particularly advantageous for high rotation motors such as high rotation. Suitable for dental motors.
For example, 30,000 to 200,000 revolutions / minute may be indicated as the speed range of this type of motor, and revolutions exceeding 200,000 revolutions / minute may be envisaged.

DESCRIPTION OF SYMBOLS 1 ... Handpiece 2 ... Handle casing 2a ... Rear area | region of a handle casing 2b ... Front area | region of a handle casing 3 ... Head area of a handpiece 4 ... Coupling element 5 ... Rule Holder 6a, 6b ... Tool holder bearing 8 ... Transmission element 10 ... Electric motor 11 ... Rotor 15 ... Drive shaft 16a, 16b ... Drive shaft bearing 17 ... Transmission element 20 ... Rotor shaft 22 ... Pressing connection between balancing ring and shaft (prior art)
22 '... Pressing connection between centering element and magnet 24,24 ... Adhesive 26' ... Pressing connection between centering element and balancing ring 28 '... Balancing ring and shaft 30 ... Connection part 31 ... Supply pipe 40 ... Magnet 45 ... Front face of centering element,
60, 60 '... centering element (first aspect)
60 "... centering element (second embodiment)
60 "... centering element (third aspect)
70 ... Ball bearing 80 ... Rotating shaft of rotor shaft 100, 100 '... Balancing ring

Claims (13)

A rotor for an electric motor,
The rotor is
A shaft (20) comprising a rotational axis (80);
A rotor having at least one magnet (40) arranged around the rotation axis (80);
The rotor has the centering element (60, 60 ′, 60 ″, 60 ′ ″) elastically connected to the shaft (20) or configured as part of the shaft 20. And
The centering element (60, 60 ′, 60 ″, 60 ′ ″) is external to the magnet (40) for centering the magnet with respect to the rotational axis (80) of the shaft (20). A rotor characterized by pressing. The rotor according to claim 1, wherein the magnet (40) is disposed on the outer periphery of the shaft (20). The centering element (60, 60 ', 60'',60''') and the magnet (40) are at least partially connected to each other by a press fit or a reduced fit. The rotor according to 2. 4. The centering element (60, 60 ′, 60 ″, 60 ′ ″) has a sleeve-like region that at least partially wraps the magnet (40) from the outside. The described rotor. Further comprising at least one balancing ring (100, 100 ') disposed on the shaft (20);
The rotor according to claim 1, wherein the centering element (60, 60 ′, 60 ″, 60 ′ ″) is elastically connected to the balancing ring 100, 100 ′. . The rotor according to claim 5, wherein the centering element (60, 60 ', 60 ", 60'") and the balancing ring (100, 100 ') are made from one piece. The centering element (60, 60 ′, 60 ″, 60 ′ ″) is press-fitted to the balancing ring (100, 100 ′) or reduced fit to the balancing ring (100, 100 ′). The rotor according to claim 5. The rotor according to any one of claims 5 to 7, wherein the balancing ring is either pressed against the shaft (20) or contracted to the shaft (20). 2. The centering element (60, 60 ′, 60 ″, 60 ′ ″) encloses the magnet over the entire range of the magnet (40) along the shaft (20). The rotor of any one of -8. The centering element (60, 60 ′, 60 ″, 60 ′ ″) encloses the magnet over the shaft (20) and partially covering the entire range of the magnet (40). The rotor according to claim 1. The rotor according to any one of claims 1 to 10, wherein an adhesive is provided between the shaft (20) and the magnet (40).   The electric motor which has a rotor of any one of Claims 1-11.   A dental handpiece comprising the electric motor according to claim 12.

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